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Re: Interesting bit of info on spark gaps and UV
On Wed, 25 Nov 1998 18:55:34 -0700, you wrote:
>Original Poster: Greg Leyh <lod-at-pacbell-dot-net>
>
>> Original Poster: "Gregory R. Hunter" <ghunter-at-enterprise-dot-net>
>>
>> "Sounds interesting - how about a small sync motor with a disk on the
>> shaft. A hole in the disk allows UV from a carbon arc to pass through
>> the disk at the appropriate instant fall onto the gap element! That
>> would be easy to build! (and it might even work)
While we're on the subject of UV, I had a few thoughts...
Does irradiating a spark gap with continuous UV significantly reduce
the gap breakdown voltage ? (If not, please ignore the rest of this
post....!)
My guess (based on gut feeling rather than expertise..) is that the
presence of UV probably wouldn't affect quenching much as the spark
produces so much UV and ionisation itself.
Perhaps a gap with a simple continuous UV source would make lower
voltage power supplies (e.g. MOTs) more viable for tesla coil use -
this would be great news for those outside the US who find NSTs hard
to get.
The six million volt question of course is how much UV do you need to
make a significant difference, and would a short-wave eprom
eraser/germicidal tube be enough?
You could very easily mount a short-wave UV tube from an eprom eraser
in the centre of a RQ/TCBOR cylindrical gap. It would of course be
very simple to evaluate whether it made any difference by comparing
results with the tube switched on and off. I'll give this a try soon
when I get time.
UV tubes will vary their output in time with the AC mains waveform,
but this would be reasonably in-phase with the gap voltage, and so
shouldn't be a problem. You could always use a high-frequency ballast
(well protected from sparks of course!).
If eprom eraser tubes prove to be effective, it could be worth
investigating alternative drive methods to provide a short, higher
powered mains-synchronous UV pulse using a triac to fire a capacitor
through the tube, maybe with a filament pre-heat supply (I guess this
would probably be necessary to vaporise the mercury). Alternatively,
maybe you could run it like a flash tube by adding an external trigger
electrode.
Another idea - at what voltage does a UV tube strike with a cold
filament ? If it's only a few KV, maybe you could simply connect it
via a resistor across the gap - as the gap voltage rises, the tube
strikes, which in turn initiates the main gap discharge - this would
be a beautifully elegant solution if it worked!